Résumé / Abstract Seminaire_IAP
« Nucleosynthesis in neutron-star mergers »

Stéphane Goriely
Inst. Astronomie Astrophysique, Univ. Libre Bruxelles (Bruxelles, Belgique)

One of the major issues in modern astrophysics concerns the analysis and understanding of the present composition of the Universe and its various constituting objects. Nucleosynthesis models aim to explain the origin of the different nuclei observed in nature by identifying the possible processes able to synthesize them. Though the origin of most of the nuclides lighter than iron through the various hydrostatic and explosive burning stages in stars is now quite well understood, the synthesis of the heavy elements (i.e. heavier than iron) remains obscure in many respects. In particular, the rapid neutron-capture process, or r-process, is known to be of fundamental importance for explaining the origin of approximately half of the A>60 stable nuclei observed in nature. The r-process was believed for long to develop during the explosion of a star as a type-II supernova but recent observations tend to favour the merging of two compact objects. In particular, the recent observation of the binary neutron star (NS) merger GW170817 and its corresponding optical kilonova counterpart suggest that neutron star mergers could be the dominant source of r-process production in the Universe.

Comprehensive nucleosynthesis calculations based on sophisticated multi-dimensional relativistic simulations of neutron star mergers are available. These include the contributions from both the dynamical (prompt) ejecta expelled during NS-NS or NS-black hole (BH) mergers, as well as the neutrino and viscously driven outflows generated during the post-merger remnant evolution of relic neutron stars or BH-torus systems. It will be shown that both contributions can lead to the production of r-process elements from Zr up to thorium and uranium with an abundance distribution that reproduces fairly well the solar distribution, as well as the elemental distribution observed in low-metallicity stars. Although neutron star mergers could explain the overall enrichment of the Galaxy in r-process elements, some open questions concerning the relevance of neutron star mergers as the main r-process sites remain. These various aspects will be discussed.
vendredi 18 octobre 2019 - 11:00
Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris
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